An organic EL device has rapidly made progress as a luminescent device with a high efficiency in recent years. The organic EL device advantageously emits light with a high brightness since it is a current-type element. However it also has the following disadvantage because of being a current-type element; current increases at a high brightness, and power consumption thus decreases due to the electric resistance of wiring.
In order to solve the disadvantage, various improvements for enhancing current efficiency have been carried out.
For example, the technique is disclosed that a plurality of organic EL devices are stacked and light emitted from each of the devices is combined, thereby enhancing current efficiency. Specifically U.S. Pat. No. 5,932,895 discloses a method of stacking RGB elements, but the method does not enhance luminous efficiency. JP-A-H11-312585, JP-A-H11-312584 and JP-A-2003-45676 disclose a structure of stacking a plurality of elements with an excellent efficiency; however they do not have a satisfactory life time.
As stated above, there remain many problems concerning the high efficiency of an organic EL device at the present.
The invention has been made in view of the above-mentioned problems and an object thereof is to provide an organic EL device with a high efficiency and long life time.
In order to attain the object, the inventors conducted various studies through which they have found that it is effective to arrange an intermediate electrode layer made of a semiconductive material with a certain resistivity between emitting layers of an organic EL device and have made the invention based on their findings.